It is known in the art to compound polymers, such as rubbers, in order to provide the rubber composition with improved properties. Fillers, reinforcing agents, anti-oxidant, curing agents and the like are often added during the compounding operations. The compound is then processed into the shape of the desired product and is vulcanized such as by heating.
It is generally known that as the mix quality or dispersion of the filler materials, such as carbon black is improved, the uniformly and hence, desirability of the end product is correspondingly improved. That is, the more uniformly the materials are dispersed, the easier it is to provide a uniform end product.
Heretofore, it has been common in the art to add rubber and pelletized carbon black together and thoroughly mix to dispense the filler throughout the rubber. Another approach has been to combine rubber particles with the filler materials, both of which must normally be reduced in size to nanometer levels. In the latter instance, it has been found that conventional mixing leads to a morphology in which the rubber particles are surrounded and coated with carbon black and other stock components. It has also been found that batches of such morphology do not lend themselves to shear mixing. The rubber particles are lubricated by the carbon black and are caused to rotate by any shear forces which may be applied, such as by mixer blades or the like. Appreciable deformation does not occur until gradually, the rubber particles, the carbon black and other stock components are caused to compact. This happens when the interfaces between the rubber particles begin to decrease in size, which may be encouraged by high temperature and pressure. Thus, much energy is often spent on achieving compaction which is a prerequisite in the prior art for the commencement of an efficient mixing process.
Various means have been employed heretofore to incorporate carbon black into elastomers and other polymers which include mechanical mixing of the polymers and carbon black in different stages in both dry and liquid phases.
U.S. Pat. No. 2,538,809 for instance, is directed toward a process for compounding rubbery polymers which employs a slurry of carbon black and water. The slurry is subsequently added to an aqueous rubber dispersion in relative proportions to provide about 10 to 60 parts by weight of carbon black per 100 parts of rubber.
U.S. Pat. No. 2,854,426 is directed toward a process for treating an aqueous coagulum of a synthetic latex. In practice, the coagulum is mechanically mixed in a closed chamber to express the water and the partially dewatered batch is subjected to continued intense shearing action until it has been transformed into a plastic sheetable mass.
U.S. Pat. No. 3,257,351, discloses a method for producing a substantially agglomerate-free dispersion of pigments such as carbon black in ethylene polymers. The process includes forming a polyethylene-carbon black masterbatch and mixing the masterbatch with a further amount of polyethylene.
U.S. Pat. No. 3,294,720 is directed toward a process for making high quality vulcanizable tire tread compositions which includes the step of mixing fine reinforcing carbon black with wet crumb rubber having a moisture content of about 5 to 15 percent.
U.S. Pat. No. 5,380,958 discloses a method of incorporating carbon black into elastomers wherein a premixed aqueous carbon black and latex liquid is subjected to pressurization and the pressurized fluid material is subsequently forced through a restricted orifice.
U.S. Pat. No. 4,876,297 discloses a method for preparing a mixture of elastomeric material and carbon black by adding a portion of the carbon black to the elastomeric material, preheating the same in a high-frequency alternating field and then adding the remainder of the carbon black.
U.S. Pat. No. 4,788,229 is directed toward a process for preparing chemically modified uncured rubber compositions of at least one elastomer and at least one filler. The steps include the preparation of first and second mixtures of elastomer, reinforcing filler and a chemical agent capable of promoting linkages between the filler and elastomer and then blending the two mixtures together.
U.S. Pat. No. 4,417,005 discloses a method for preparing a rubber composition for tire treads. The rubber comprises an oil extended styrene-butadiene copolymer and at least one other diene rubber. The method is practiced by incorporating part or all of at least one of the rubber components with the carbon black, and mechanically mixing together followed by the addition of the balance of the rubber components.
U.S. Pat. No. 4,395,501 provides a process for producing a vulcanizate having improved properties. Two or more C.sub.4 or C.sub.5 conjugated diolefin containing polymers are mixed together with carbon black and other compounding ingredients except cure active agents. More particularly, a portion of one or more of the polymers is mixed with a portion of all of the carbon black and other compounding ingredients, followed by the addition of the remaining polymers, carbon black, if any, and compounding ingredients. The resulting mass is allowed to rest and is then compounded with the cure active agents, it is shaped and finally vulcanized.
U.S. Pat. No. 4,321,168 discloses a similar process for preparing tire tread compositions which comprise a substantially amorphous polybutadiene and natural rubber and/or 1,4-polyisoprene and carbon black. The process includes the steps of mechanically compounding a portion of the rubber with a portion of all of the carbon black and then adding the remainder of the rubber and carbon black, if any, and mechanically compounding the mass.
U.S. Pat. No. 4,098,715 is directed toward a process for blending liquid rubber and carbon black. The carbon black is initially dispersed in a liquid rubber by mixing 60 to 150 parts by weight of carbon black with 100 parts by weight of liquid rubber and then diluting the resulting dispersion with more liquid rubber to yield a final proportion of less than 50 parts of carbon black per 100 parts of liquid rubber.